The invention relates to an engine valve actuation device, especially for actuating poppet valves. The engine valve actuation device may be arranged to supply intake gas (air plus maybe EGR) or evacuating exhaust gases from a combustion cylinder.
Internal, combustion engines typically use either a mechanical, electrical, or hydro-mechanical valve actuation system to actuate the engine valves. These systems may include a combination of camshafts, rocker arms and push rods that are driven by the engine's crankshaft rotation. When a camshaft is used to actuate the engine valves, the timing of the valve actuation may be fixed by the size and location of the lobes on the camshaft.
For each 360 degree rotation of the camshaft, the engine completes a full cycle made up of four strokes (i.e., expansion, exhaust, intake, and compression). Both the intake and exhaust valves may be closed, and remain closed, during most of the expansion stroke wherein the piston is traveling away from the cylinder head (i.e., the volume between the cylinder head and the piston head is increasing). During positive power operation, fuel is burned during the expansion stroke and positive power is delivered by the engine. The expansion stroke ends at the bottom dead center point, at which time the piston reverses direction and the exhaust valve may be opened for a main exhaust event. A lobe on the camshaft may be synchronized to open the exhaust valve for the main exhaust event as the piston travels upward and forces combustion gases out of the cylinder. Near the end of the exhaust stroke, another lobe on the camshaft may open the intake valve for the main intake event at which time the piston travels away from the cylinder head. The intake valve closes and the intake stroke ends when the piston is near bottom dead center. Both the intake and exhaust valves are closed as the piston again travels upward for the compression stroke.
The valve actuation system may further provide for variable valve lift duration as function of engine operating conditions such as speed, load, transient versus steady state, cold start versus hot condition, i.e. variable Miller operation, in order to achieve a good trade off between engine fuel efficiency, maximum peak cylinder pressure, gaseous emission, exhaust gas temperature (temperature suitable for emission catalyst system). Variable valve lift duration may be achieved via a camshaft arrangement with concentric camshafts.
U.S. Pat. No. 8,820,281 discloses a camshaft for an internal combustion engine, having a hollow outer shaft and an inner shaft which is concentrically mounted inside the outer shaft to be rotatable about an angle and a multi-part cam element having a first cam section that is mounted on the outer shaft in a rotationally fixed manner and a second cam section that is connected to the inner shaft in a rotationally fixed manner and rotationally mounted on the outer shaft. The two cam sections have different cam contours, the relative movement of the two cam sections in opposite directions allowing the resulting cam contour of the cam element interacting with a cam follower to be changed to adjust the variable valve opening period. The two cam sections have different maximum lifts, the cam top section of the cam section having the smaller maximum lift being substantially formed by an annular sector.
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as passenger cars, buses and construction equipment. Further, the invention will be described with examples to supply intake gas (air plus maybe EGR), but may alternatively be used for evacuating exhaust gases from a combustion cylinder.
It is desirable to provide an engine valve actuation device, which creates conditions for varying a valve lift duration in a robust way.
According to an aspect of the invention, a device for actuating at least one valve in an internal combustion engine comprises    a camshaft arrangement comprising    a hollow outer shaft,    an inner shaft, which is concentrically mounted inside of the outer shaft to be pivotable relative to the outer shaft,    a first cam lobe mounted on one of the inner shaft and the outer shaft in a rotationally fixed manner,    a second cam lobe mounted on the other of the inner shaft and the outer shaft in a rotationally fixed manner,    a rocker arm arrangement comprising    a first primary rocker arm, which is arranged to follow the first cam lobe and arranged to actuate a first valve when it follows the first cam lobe,    characterized in that    the rocker arm arrangement comprises    an auxiliary rocker arm, which is arranged to follow the second cam lobe and that the auxiliary rocker arm is adapted to actuate the first primary rocker arm so that an opening time of the first valve may be extended by the auxiliary rocker arm following the second cam lobe.
This device creates conditions for a variable intake valve lift duration, and especially an extension of a duration of the valve opening time for late closing of the valve, i.e. variable Miller operation. In other words, a delayed closing time may be achieved. According to an alternative, the device may be used for an extension of a duration of the valve opening time via a pre-opening of the valve. In other words, an early opening time may be achieved.
The auxiliary rocker arm and the second cam lobe are adapted for supporting the primary rocker arm and the first cam lobe in the actuation of the first valve. According to one example, the pair of the auxiliary rocker area and the second cam lobe has a supporting function only in the extension of the opening time of the first valve. According to one example, the term “auxiliary” defines that the auxiliary rocker arm does not have any dedicated own valve, but instead is adapted to support in the extension of the opening time of the first valve (and possibly a further valve). The arrangement of the auxiliary rocker arm and the second cam lobe creates conditions for adapting the device for different needs in different engines by different designs of the profile of the second cam lobe.
The camshaft arrangement may be called concentric camshafts. According to one example, a cam phaser arrangement is adapted to pivot the inner shaft in relation to the outer shaft to different relative positions in order to vary the relative positions of the first cam lobe and the second cam lobe.
According to one example, the second cam lobe is arranged adjacent the first cam lobe. Similarly, the auxiliary rocker arm is arranged adjacent the first primary rocker arm. According to a further example, an axial distance between the second cam lobe and the first cam lobe matches a distance between a centre plane of the auxiliary rocker arm and a centre plane of the first primary rocker arm (the centre plane being in parallel with a pivoting motion of the respective rocker arm).
According to one example, the auxiliary rocker arm has a free end opposite the end following the second cam lobe, wherein the free end is not adapted to actuate any further valve. According to a further example, the auxiliary rocker arm is arranged in parallel with the first primary rocker arm but while a plane defined by a pivoting motion of the first primary rocker arm matches the first valve, a plane defined by a pivoting motion of the auxiliary rocker arm is not matched to any valve. According to a further example, an engine cylinder is provided with two inlet valves, wherein the plane defined by the pivoting motion of the first primary rocker arm matches a first one of the two inlet valves and wherein the plane defined by a pivoting motion of the auxiliary rocker arm is inbetween the two inlet valves. According to a further example, the plane defined by the pivoting motion of the first primary rocker arm matches a centre point of the first one of the two inlet valves and the plane defined by the pivoting motion of the auxiliary rocker arm is offset in relation to the centre point of the first inlet valve.
According to one embodiment, the first cam lobe and the second cam lobe have different cam profiles. The first cam lobe may be adapted for a main intake event. The second cam lobe may be adapted for extending the main intake event for achieving a Miller operation by varying the relative circumferential positions of the inner shaft and the outer shaft.
According to a further embodiment, the first cam lobe has a symmetrical shape with regard to a peak point of the first cam lobe. Preferably, the first cam lobe has a continuously rounded contour. More specifically, the first cam lobe may have a conventional shape.
According to a further embodiment, the second cam lobe has a non-symmetrical shape with regard to a peak point of the second cam lobe. According to one example, the second cam lobe has a substantially planar profile part in the form of a slope. This design creates conditions for a smooth transition between valve actuation controlled by the first cam lobe and the second cam lobe during operation. According to a further development of the last mentioned example, the substantially planar profile part has a first end and a second end, which are at different lift heights. According to one example, the device is adapted for achieving a smooth transition between valve actuation controlled by the first cam lobe and the second cam lobe, which is described below.
According to a further embodiment, the first cam lobe and the second cam lobe have different maximum lift heights. According to one example, the first cam lobe has a higher maximum lift height than the second cam lobe.
According to a further embodiment, the device comprises a damping arrangement for damping a transition at a transfer point, at which a change of valve opening activation takes place from the first cam lobe to the second cam lobe. Such a damping arrangement creates conditions for a variety of different combinations of cam lobe designs. According to one example, the auxiliary rocker arm comprises at least a part of the damping arrangement. Positioning the damping arrangement in the auxiliary rocker arm creates conditions for a space-efficient device. According to a further example, the damping arrangement comprises a hydraulic circuit. A hydraulic circuit has turned out to be efficient and reliable for valve actuation.
According to a further embodiment, the damping arrangement comprises a first contact member for contacting the first primary rocker arm in order to actuate the first primary rocker arm. Thus, the contact member is adapted to transfer the actuation of the valve from the first primary rocker arm riding on the first cam lobe to the auxiliary rocker arm riding on the second cam lobe. According to one example, the first contact member is moveably arranged in the auxiliary rocker arm. According to a further embodiment, the first contact member is formed by a piston in the hydraulic circuit. Thus, by pressurizing a hydraulic fluid, the piston may be moved to a projected position, in which it will contact the first primary rocker arm and actuate it when the auxiliary rocker arm rides on the second cam lobe.
According to a further embodiment, the first primary rocker arm comprises a first contact portion and the auxiliary rocker arm comprises a second contact portion and wherein the first primary rocker arm and the auxiliary rocker arm are arranged in relation to one another so that the first and second contact portions may be in contact for achieving that the opening time of the first valve is extended by the auxiliary rocker arm following the second cam lobe. Thus, the first contact portion and the second contact portion are arranged so that they face each other for engagement during a relative movement of the first primary rocker arm and the auxiliary rocker arm.
According to a further development of the last mentioned embodiment, the first and second contact portions are in contact with each other when the first primary rocker arm and the auxiliary rocker arm are moved relative to one another in a first direction and wherein the first and second contact portions are free from contact with each other when the first primary rocker arm and the auxiliary rocker arm are moved relative to one another in a second direction, opposite the first direction.
According to a further embodiment, the first moveably arranged contact member comprises the second contact portion.
According to a further embodiment, the first primary rocker arm has a main extension direction in a transverse direction in relation to a rotational axis of the camshaft arrangement, wherein the first primary rocker arm comprises a boss projecting in a transverse direction in relation to the main extension direction and wherein the boss comprises the first contact portion.
According to a further embodiment, the device is arranged so that an opening time of the first valve may be controlled via the second cam lobe by pivoting the inner shaft relative to the outer shaft to different relative circumferential positions.
According to a further embodiment, the device comprises an arrangement for pivoting the inner shaft relative to the outer shaft to different relative circumferential positions and allowing the inner shaft and the outer shaft to rotate with same speed in the different relative circumferential positions. Such a pivoting arrangement may be called a “cam phaser”. According to one example, the pivoting arrangement is arranged at one end of the cam shaft arrangement and comprises a hydraulic system for pivoting the shafts relative to one another.
According to a further embodiment, the camshaft arrangement comprises a third cam lobe mounted on the same shaft of the inner shaft and the outer shaft as the first cam lobe in a rotationally fixed manner, wherein the rocker arm arrangement comprises a second primary rocker arm, which is arranged to follow the third cam lobe and arranged to actuate a second valve when it follows the third cam lobe and wherein the auxiliary rocker arm is adapted to actuate the second primary rocker arm so that an opening time of the second valve may be extended by the auxiliary rocker arm following the second cam lobe. Thus, auxiliary rocker arm is adapted to effect both the first primary rocker arm and the second primary rocker arm, which creates conditions for a space-efficient design. Preferably, the device is adapted so that the auxiliary rocker arm effect the first primary rocker arm and the second primary rocker arm simultaneously and in the same way. Thus, in this way, two intake valves of an engine cylinder may be actuated simultaneously and in the same way.
According to a further development of the last mentioned embodiment, the third cam lobe is positioned on an opposite side of the second cam lobe in relation to the first cam lobe. Further, the second primary rocker arm is positioned on an opposite side of the auxiliary rocker arm in relation to the first primary rocker arm.
According to a further example, an engine cylinder is provided with two inlet valves. According to a further example, the second primary rocker arm is arranged in parallel with the first primary rocker arm and at a distance matching the distance between the two inlet valves so that the second primary rocker arm is arranged to actuate the second valve. In other words, a plane defined by a pivoting motion of the second primary rocker arm matches the second valve. According to a further example, the plane defined by the pivoting motion of the second primary rocker arm matches a centre point of the second one of the two inlet valves.
According to a further development of the last mentioned embodiment, the second primary rocker arm has a main extension direction in a transverse direction in relation to a rotational axis of the camshaft arrangement, wherein the second primary rocker arm comprises a boss projecting in a transverse direction in relation to the main extension direction and wherein the boss comprises a third contact portion for contacting the second contact portion of the auxiliary rocker arm. According to one example, the boss of the second primary rocker arm projects in an opposite direction relative to the boss of the first primary rocker arm so that the ends of the bosses meet, preferably with a small gap.
According to a further development of the last mentioned embodiment, the first cam lobe and the third cam lobe are substantially identical.
According to a further embodiment, the rocker arm arrangement comprises a rocker arm shaft and wherein at least one of the rocker arms is pivotally arranged on said shaft.
According to a further embodiment, the rocker arm shaft is arranged in parallel with the camshaft arrangement.
According to a further aspect, the invention is related to an internal combustion engine comprising a cylinder provided with at least one intake valve and at least one exhaust valve and an engine valve actuation device according to any one of the above alternatives for actuating at least one of said valves.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.